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Difficulty: MediumLogical Inferences

Plants often defend against herbivores by emitting volatile organic compounds (VOCs) that recruit predatory insects. Producing VOCs requires significant nitrogen, a nutrient essential for plant growth. In a study of *Solanum lycopersicum* (tomato plants), researchers observed that plants grown in nitrogen-deficient soil reduced their VOC emissions by over 60% when attacked by caterpillars, compared to plants in nitrogen-rich soil. However, the nitrogen-deficient plants showed a corresponding increase in the production of glandular trichomes (hair-like structures on leaves), which physically impede herbivores and are composed primarily of carbon. Because carbon is abundant even in nutrient-poor soils, researchers concluded that under nitrogen limitations, *Solanum lycopersicum* shifts its defense strategy. Which choice most logically completes the text?

  1. A
    to prioritizing the conservation of nitrogen by suspending all leaf-level defense mechanisms until soil nutrient levels improve.
  2. B
    by increasing VOC emissions specifically during the early stages of caterpillar feeding to compensate for the nitrogen deficiency.
  3. away from chemical signals that recruit predatory insects and toward physical structures that hinder pests directly.Answer
  4. D
    toward attracting predatory insects that are capable of digesting carbon-rich physical barriers instead of relying on VOC cues.

Answer

The correct answer states that under nitrogen limitations, *Solanum lycopersicum* shifts its defense strategy away from chemical signals that recruit predatory insects and toward physical structures that hinder pests directly.
The passage establishes that VOC production (which recruits predatory insects) is nitrogen-dependent and decreases significantly under nitrogen deficiency. Conversely, the production of glandular trichomes (physical barriers) is carbon-based and increases because carbon is abundant. Therefore, the plant shifts its defense strategy away from the nitrogen-intensive chemical attraction of predators toward carbon-based physical barriers that directly obstruct herbivores.

Step-by-Step Solution

1
Identify the two defense mechanisms described in the passage.
The plant utilizes volatile organic compounds (VOCs) to attract predators, and glandular trichomes to physically block herbivores.
Establishing the options for defense is necessary to track how the plant's behavior changes.
2
Analyze the resource constraints for each defense mechanism.
VOCs are nitrogen-dependent, and nitrogen is scarce in poor soils. Glandular trichomes are carbon-based, and carbon is abundant even in poor soils.
Understanding the resource availability explains why the plant cannot maintain both defenses equally.
3
Evaluate the observed shift in the plant's response under nutrient limitation.
When nitrogen is limited, the plant reduces its nitrogen-costly VOC emissions by over 60% but increases its carbon-based trichomes.
Synthesizing these observations leads to the logical conclusion that the plant shifts its strategy from the chemical recruitment method to the physical barrier method.

Key Concept

Logical Inferences under resource constraints
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Topics

Logical Inferences

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